(Meth)acrylic acid is generally prepared by gas phase oxidation of propane, propylene, (meth)acrolein, and the like in the presence of a catalyst. For example, propane, propylene, and the like are converted to (meth)acrylic acid through (meth)acrolein by gas phase oxidation in the presence of an appropriate catalyst in a reactor, and a mixed gas (1) including (meth)acrylic acid, non-reacted propane or propylene, (meth)acrolein, an inert gas, carbon dioxide, water vapor, and various organic byproducts (acetic acid, heavies, and the like) is obtained in the back end of the reactor.
The (meth)acrylic acid-containing mixed gas (1) contacts an absorption solvent such as process water in a (meth)acrylic acid absorption tower (100), and is recovered as a (meth)acrylic acid aqueous solution. Further, a (meth)acrylic acid-stripped insoluble gas is recycled for a synthesis reaction of (meth)acrylic acid, and a part thereof is incinerated and discharged. The (meth)acrylic acid aqueous solution is distilled and purified to obtain (meth)acrylic acid.
Meanwhile, various methods of controlling process conditions or process sequences and the like to improve the recovery efficiency of (meth)acrylic acid have been suggested. Representatively, as a method for separating water and acetic acid from the (meth)acrylic acid aqueous solution obtained in the (meth)acrylic acid absorption tower (100), an azeotropic distillation method using a hydrophobic solvent in a distillation column is known. As another method, a (meth)acrylic acid aqueous solution is fed to a (meth)acrylic acid extraction tower (200), and using a hydrophobic solvent, a (meth)acrylic acid extract solution with reduced water content and a raffinate solution thereof are obtained, and the extract is distilled, thereby reducing energy consumption.
However, in the known method of recovering (meth)acrylic acid, the (meth)acrylic acid absorption tower (100) discharges the aqueous solution of a single stream to the lower part, and there are limitations in that if the concentration of discharged (meth)acrylic acid aqueous solution is to be increased, the separation efficiency of the (meth)acrylic acid absorption tower (100) may be lowered, and if the concentration of discharged (meth)acrylic acid aqueous solution is maintained low so as to increase separation efficiency, purification (or distillation) load in the subsequent purification (or distillation) process may increase.